.TH SKEWEDIT 1 "31 July 2002" "WFDB 10.2.7" "WFDB Applications Guide"
.SH NAME
skewedit \- edit skew fields of header file(s)
.SH SYNOPSIS
\fBskewedit\fR \fIrecord skew0\fR [ \fIskew1 ... skewN\fR ]
.SH DESCRIPTION
This program reads the \fBheader\fR(5) file for the specified \fIrecord\fR,
changes the skew fields to match the \fIskew0\fR, \fIskew1\fR,
etc. arguments, and rewrites the header file as \fIrecord\fR.hea in
the current directory.  \fIskew0\fR is the skew in samples for signal 0,
\fIskew1\fR is the skew for signal 1, etc.  Skews may not be negative;
any omitted skews are taken to be zero.
.PP
Skew refers to time differences between samples having the same sample
number in different signals.  Skew may arise while digitizing
multitrack analog tape recordings, for example, as a result of
differences in the azimuth of the recording and playback heads of the
recording equipment.  It may be possible to measure skew (for example,
by applying test signals simultaneously or at known intervals to all
input channels, and then by measurement of the digitized test
signals).  When this is possible, \fIskewedit\fR can then be used to
record the skew measurements in the header file.
.PP
For example, assume that a test signal applied simultaneously to all
inputs of record \fIabc\fR is determined to appear on signal 0 at
sample 30, on signal 1 at sample 28, on signal 2 at sample 28, and on
signal 3 at sample 26.  In this case, \fIskew0\fR is 4 (30 - 26),
\fIskew1\fR and \fIskew2\fR are each 2, and \fIskew3\fR is 0.  The
command
.br
	\fBskewedit abc 4 2 2 0\fR
.br
would apply the proper correction to the header file for the record.
(The final `0' may be omitted from the command.)
.PP
Applications built using the WFDB library (version 9.2 or later) are
able to correct for skew (the skew correction is performed by the WFDB
library and is not visible to the application program).  Note that
skew correction does not require rewriting the signal file(s).
.PP
If you wish to create skew-corrected signal files (for example, to use
with applications built using earlier versions of the WFDB library), use
\fBxform\fR(1) to do so, using the header file generated by
\fBskewedit\fR as input to \fBxform\fR.  Note, however, that older
applications can generally be updated without source changes simply
by recompiling them and linking them with the current WFDB library.
.SH ENVIRONMENT
.PP
It may be necessary to set and export the shell variable \fBWFDB\fR (see
\fBsetwfdb\fR(1)).
.SH SEE ALSO
\fBsetwfdb\fR(1), \fBxform\fR(1), \fBheader\fR(5)
.SH AUTHOR
George B. Moody (george@mit.edu)
.SH SOURCE
http://www.physionet.org/physiotools/wfdb/app/skewedit.c
